Venting cryosurgical instrument

ABSTRACT

The cap which is threaded onto the dewar of a cryosurgical instrument has a vent hole therethrough which is normally closed off by a gasket when the cap is secured to the dewar, but which can allow the venting of gaseous cryogen therethrough when the cap is loosened. The threads of the cap have a scalloped region in which the threads have been machined away so as to provide a passage for gaseous cryogen, whereby, when the cap is loosened on the dewar, pressure therein is released by gas escaping either through the hole or through the scalloped region of the threads.

RELATED INVENTIONS

The subject matter herein relates to commonly owned, copending U.S.patent applications filed contemporaneously herewith entitled"Cryosurgical Instrument", Serial No. D-(Docket No. B-44) and entitled"Fail-Safe Cryosurgical Instrument", Serial No. (Docket No. B-46).

TECHNICAL FIELD

This invention relates to relieving the pressure within the dewar of acryosurgical instrument as the dewar cap is loosened.

BACKGROUND ART

A cryosurgical instrument disclosed in U.S. Pat. No. 4,269,390 employinga standard, double walled, evacuated, metal vacuum bottle or dewar, hasa collar metallurgically bonded to the top of the dewar near the mouththereof to provide machine threads for releasably engaging the deliveryand control portion of the instrument, which is mounted on a cap havinginternal threads, to the dewar of the instrument. The cap has a valvemounted thereon which controls the flow of nitrogen from a feed tube inthe dewar to a nozzle mounted on a delivery tube. The valve is opened bya valve operating lever. The cryosurgical instrument of said patent hasbeen in service around the world, with minor modifications, since 1976.

In order to avoid explosive splashing of cryogenic liquid when the capis removed from the dewar of such an instrument, it has been common inthe past to lift the cap of a pressure relief valve, thereby allowinggaseous cryogen to escape, relieving the pressure within the dewar. Withthe advent of more streamlined pressure relief valves, however, themovement of the pressure relief valve to relieve pressure within thedewar became difficult, and created the risk of undesirable freezing ofthe skin as a consequence of cold cryogenic gas emanating from thevalve. In an attempt to overcome this problem, the threads of the caphave been machined away at one point, so as to provide a passage for theescape of gas once the cap was loosened sufficiently to allow gas topass by a gasket, such as one-quarter or one-half of a turn. However, itwas found that this expedient worked sometimes, but more frequently didnot work, so that the operator frequently had to revert to raising ofthe pressure relief valve in order to release the pressure in the dewar.

DISCLOSURE OF INVENTION

Objects of the invention include improved venting of the dewar of acryosurgical instrument when the cap is being removed.

This invention is predicated in part on the discovery that gas pressurewithin the dewar acting against a gasket within the dewar cap may causethe gasket to block the passage formed by machining away a small sectionof threads, thereby not allowing gas to be vented to depressurize thedewar as a consequence of turning the cap.

According to the present invention, the cap of the dewar of acryosurgical instrument has a hole therethrough which is normallyblocked by the gasket when the cap is tightened on the dewar, but whichcan release gas when the cap is loosened sufficiently for the gasket toclear the hole, the cap also having a scallop shaped passage formed bymachining away the threads of the cap in the vicinity of theaforementioned hole. The invention, by having both the passage formed inthe threads and a passage formed by a hole in the cap, the two passagesbeing within a workable distance of each other, always provides one oftwo paths for gas to escape. If the gasket is blocking the passagethrough the threads, when the cap is loose, it cannot be blocking thehole through the cap. Similarly, when the cap is loosened, if the gaspressure keeps the gasket pressed against the hole, thereby sealing it,it cannot be blocking the passage through the threads. Thus, a quarteror half turn of the cap will always result in depressurizing the dewar,in every case.

Other objects, features and advantages of the present invention willbecome more apparent in the light of the following detailed descriptionof exemplary embodiments thereof, as illustrated in the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a cryosurgical instrument incorporatingthe present invention.

FIG. 2 is a partial, partially sectioned, partially broken away bottomplan view of the cap of the cryosurgical instrument of FIG. 1.

FIG. 3 is a sectioned side elevation view taken on the line X--X in FIG.2.

FIG. 4 is a partial sectioned side elevation view taken on the line X--Xin FIG. 2, and the top of the dewar, with a gasket blocking the ventingof gaseous cryogen through the passage in the threads of the cap whilepassing the gaseous cryogen through a hole.

FIG. 5 is a partial, sectioned side elevation view taken on the lineX--X of FIG. 2, and the top of the dewar, with a gasket blocking theventing of gaseous cryogen through a hole, but allowing the gaseouscryogen to flow through a passage in the threads of the cap.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, a cryosurgical instrument in which the presentinvention may be practiced includes a dewar 6, at the opening of whichare threads to receive a threaded cap 7 which comprises the delivery andcontrol portion of the instrument. The cap 7 has a main valve 8 disposedthereon, the valve having a valve operating lever 10 working with afulcrum 11 to raise a stem 12 of a valve so as to regulate the flow ofcryogenic fluid from within the dewar 6 along a feed tube 15 into adelivery tube 16 to a nozzle 17. The fluid pressure within the dewar 6is maintained by a pressure relief valve 18. The functions, although notthe appearance, of the instrument as thus far described are similar tothose in said patent.

Referring to FIGS. 2-5, the cap 7 has internal threads 20 which capturea gasket 21 which usually overlies a hole 23, thereby blocking the holewhen the cap 7 is screwed tightly to the dewar 6. The threads 20 have ascallop portion 24, in which the threads have been machined away, so asto provide a passage for gaseous cryogen down through the cap, when thecap 7 is loosened on the dewar 6, and the gasket 21 is being held upagainst the hole 23 by gaseous pressure, as shown in FIG. 5. On theother hand, should the gasket fall downwardly, when the cap is loosenedon the dewar, the gaseous cryogen can flow past the gasket and out thehole 23, as shown in FIG. 4.

The main valve 8 and pressure relief valve 18 in this embodiment, areheld to the cap 7 by means of corresponding nuts 30, 31, as seen in FIG.2. However, the invention may be practiced with valves secured to thecap in other ways.

As is seen in FIGS. 2-5, the scallop area 24 should be rather close tothe hole 23 so that if the hole is blocked, the scallop axiomaticallywill not be blocked, and vice versa, as illustrated by comparing FIGS. 4and 5. On the other hand, it is not necessary that the scalloped area 24be perfectly aligned with the hole 23, as shown. In the embodimentherein, the hole 23 is positioned directly beneath the feed tube 16.This is to cause any gas which emanates through the hole 23 to bedispersed, thereby providing the least risk to the operator. However,the invention may be practiced with the hole in a different positionrelative to the feed tube 16 or other components on the cap 7.

In the present embodiment, the hole 23 is drilled through the topsurface of the cap. However, the invention may as readily be practicedwith the hole located in the rim of the cap, provided such hole can ventthe cryogen (in a manner obvious when viewing FIG. 4). As seen in FIG.2, the scalloped area 24 does not, in this embodiment, completelyobliterate the threads in the vicinity of the hole 23. However, it maybe preferable to have the scalloped area 24 deeper, thereby totallyeliminating the threads in that region, and possibly even cutting intothe rim of the cap.

Thus, although the invention has been shown and described with respectto exemplary embodiments thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, withoutdeparting from the spirit and scope of the invention.

I claim:
 1. A cryosurgical instrument comprising:a dewar for containingliquid cryogen, the mouth of said dewar having threads; a cap havingthreads complementary to the threads on said dewar, said cap having adelivery and control portion of the cryosurgical instrument disposedthereon; and a gasket within said cap; wherein the improvementcomprises:a vent hole positioned in said cap over said gasket; and ascalloped region in the vicinity of said vent hole, said scallopedregion consisting of an area of said cap where said threads have beenmachined away to provide a passageway for gaseous cryogen, whereby, whenthe cap is loosened on the dewar, gaseous cryogen may escape around thegasket either through said hole or through said scalloped region,thereby releasing the pressure in said dewar.
 2. The instrumentaccording to claim 1 wherein the center of said scalloped region and thecenter of said hole are disposed substantially on the same major axis ofsaid cap.
 3. An instrument according to claim 1 wherein said hole isdisposed in a top surface of said cap immediately above said scallopedarea.